1. Field of the Invention
The present invention relates to a crack growth evaluation apparatus, a crack growth evaluation method, and a recording medium recording a crack growth evaluation program. More specifically, the present invention relate to a crack growth evaluation apparatus, a crack growth evaluation method, and a recording medium recording a crack growth evaluation program capable of evaluating with high accuracy the growth of a crack occurring in a continuum in a finite element method.
2. Description of the Related Art
For a solder material and various types of joining resin material (adhesive), stable connection reliability of a junction is important. Practically, it is necessary for a connected portion to have sufficient durability in the temperature cycle and the mechanical cycle of oscillations and so on cyclically applied in an actual use environment. In the designing stage of a connected portion, there is a method for calculating a stress and a distortion by performing a simulation using a finite element method and so on, and indirectly evaluating the life and so on based on the calculated stress and distortion values. The method has been conventionally used in many parts and device development evaluations. Especially, in estimating the count of the cyclic fatigue life such as temperature cyclic fatigue, a method for estimating the cyclic fatigue life count using a Manson-Coffin law based on a distortion value obtained from a simulation result using the finite element method and so on.
FIG. 25 is a diagram showing an analysis model of a soldered portion. An analysis model of a soldered portion 102 is used in a simulation performed in the finite element method and so on. In a conventional method, the following equation 1 calculates Nf as the count of cyclic fatigue life in the Manson-Coffin law by obtaining a distortion amplitude value Δεin for the finite element of the portion enclosed by the circle in bold type using the analysis model.Nf=½·(Δεin/εo)−n   (equation 1)In the equation 1, n and ε0 are parameters depending on the material and shape of the soldered portion 102.
Proposed is a system of calculating an amount of distortion occurring at a soldered portion in electronic equipment configured by a wiring substrate whose opposing surfaces have electronic parts attached through a soldered portion by inputting optional position related information among electronic parts to a stress curve displayed with an amount of distortion occurring at a soldered portion being associated with position related information among electronic parts (refer to the Japanese Patent No. 3900042).
The conventional technique for calculating the count of cyclic fatigue life Nf based on the finite element method and the Manson-Coffin law (hereinafter referred to simply as conventional technique) evaluates a life using stress and distortion occurring at a soldered portion having an initial shape. Therefore, when a crack occurs in a soldered portion, the count of cyclic fatigue life can be estimated.
However, in the conventional technique, since an initial shape (produced shape) is used as the shape of an analysis model of a soldered portion, it is difficult to assume the state of a stress when a crack develops in the soldered portion. In addition, several hundreds to several tens of thousands cycles are repeated in a temperature cycle and a mechanical cycle test. However, a current computer requires several hours to several days to complete a one cycle process. Therefore, it requires quite a long time and is not practical for a computer to iteratively execute several hundreds cycles. Accordingly, with the conventional technique, it is practically difficult to estimate a complete fracture life until the final fracture after the growth of a crack in the soldered portion and to estimate the growth process of a crack.
In addition, if a simulation result is different from an actual measurement result when a growth process of a crack occurring in a continuum such as a soldered portion and so on is simulated in the conventional technique, the simulation result is not corrected based on the actual measurement result.
Furthermore, in the conventional technique, when a growth rate of a crack occurring in a continuum is obtained based on a simulation result of a growth process of a crack occurring in the continuum, the growth rate of a crack cannot be automatically obtained. Therefore, it is necessary to temporarily display the data indicating the crack (for example, data of a cumulative damage value of finite elements obtained by dividing a continuum) on a display screen, and actually measure the length of the crack on the display screen. Accordingly, the growth of a crack occurring in a continuum cannot be accurately evaluated in the conventional technique.